As used herein, the term "cable" means any manner of wire or cable, now known or later developed, including cable for the conduction of electromagnetic and/or optical energy such as, fiber optics, electrical conductive wire or other flexible material. The term "duct" means any enclosed canal, conduit, duct, tubing or other enclosed stricture that may be scaled and in which cable may typically be inserted or laid.
There exists a need for an economical and efficient process for installing cables of 3,000 feet or more in length in vertical ducts and in tubing previously installed in pipelines and well casings in gas, oil and geothermal fields. The cable typically provides means for monitoring the conditions at distant locations or in wells at significant depths below the surface. There are various methods that have been used to install cable in ducts. One such method is to cause a fluid such as water to flow through the duct, placing a drogue on the cable, then inserting the cable into the fluid flow such that such fluid flow will propel the cable through the duct by means of pressure against the drogue. Typically such methods are employed to insert the cable in horizontal duct where the cable will exit from a duct at a location downstream from the entry point. In situations where is desirable to insert the cable into a well casing installed in a gas, oil, or geothermal well, it is not uncommon for weights to be attached to the distal end of the cable in order to counter the pressure opposing the insertion. A problem with this method of insertion is that the larger the size of the cable, and the more weight is required in order to overcome the opposing pressure in the well, which weights can affect the structural integrity of the cable.
U.S. Pat. No. 5,156,376 describes a method of installing cable in pipelines, the cable having a syntactic foam pressure resistance sheath, inlet and outlet tubes in the pipeline, the cable having flexible cup members which provide viscous drag on the cable, and then extracting the cable from the downstream outlet. The foam surface of the cable is intended to provide a surface that would provide some dragging force with the flow of fluid, however, the major impetus for the cable in the pipeline being the viscous drag on the cup members by the fluid flowing in the pipeline.
Another example of the prior art for well casing applications is described in U.S. Pat. No. 5,503,370 wherein a cable is inserted into a reel coiled tubing by means of a capstan drive within a pressure housing. The tubing is then attached to other tubing being installed in a well casing, or fed down independently into the casing. The major drawback to this method is that insertion of the cable occurs on the surface, and the method does not demonstrate any advantages over the prior art in inserting cable in a duct or tube previously installed in a well casing wherein there exists a pressure within the well casing opposing the insertion of the cable.
None of the prior art or referenced patents disclose a method and apparatus for economically and efficiently inserting a flexible cable in a duct or tube wherein there is a pressure in the tube from opposing forces.